envelope-addr

Minimal parsing and formatting for SMTP envelope addresses.

This crate handles only what SMTP actually uses in commands like MAIL FROM and RCPT TO. It intentionally does not implement RFC 5322 header mailboxes.

What it supports

Accepted forms:

• local@domain
• <local@domain>
• <> (null reverse-path, used for bounces)

Behavior:

• Leading/trailing whitespace is trimmed
• Domain is ASCII-lowercased when possible
• Local part case is preserved
• Unicode local parts and domains are allowed (no IDNA conversion)

What it rejects

• Display names (Name <user@domain>)
• Comments
• Quoted local parts
• Whitespace inside the address
• Header-only mailbox syntax

If it wouldn’t appear in an SMTP command, it doesn’t belong here.

Example

use envelope_addr::Addr;

let addr = Addr::parse_envelope(" <User@Example.COM> ")?;
assert_eq!(addr.local, "User");
assert_eq!(addr.domain, "example.com");
assert_eq!(addr.to_addr_spec(), "User@example.com");
assert_eq!(addr.to_bracketed(), "<User@example.com>");

Null reverse-path:

let null = Addr::parse_envelope("<>")?;
assert!(null.is_null());

Design goals

• Small, dependency-light
• Deterministic and fully unit-testable
• Suitable for MTAs, milters, SMTP proxies, and SRS implementations
• Clear separation between envelope parsing and higher-level mail logic

Non-goals

• RFC 5322 compliance
• Header parsing
• Address normalization beyond SMTP needs

License

Licensed under the MIT license